The invention relates to barium titanate thin films and plates and to semiconductor devices such as microminiature, large capacitance capacitors using such films. The invention further relates to barium titanate thin films and plates incorporating a non-reactive electroconductive material, xe2x80x9cMxe2x80x9d. The storage capacity of the thin films and plates of the invention is at least 1 farad/cm3. The invention further relates to a method of preparing the thin films. Such crystalline thin films are characterized by a perovskite structure and have utility in the manufacture of a wide variety of ferroelectric, dielectric, pyroelectric, piezoelectric and electro-optic devices, such as nonvolatile semiconductor memories, thin-film capacitors, pyroelectric (IR) detectors, sensors, surface acoustic wave substrates, optical waveguides, optical memories, spatial light modulators as well as frequency doublers for diode lasers.
In the past years, there has been extended efforts in the development of high capacitance electrochemical energy storage devices, especially capacitors and batteries, for use in reduced volumetric areas. Both capacitors and batteries store energy by the separation of positive and negative charges. The need to store greater amounts of energy in a smaller package continues to drive new research.
Barium titanate (BaTiO3) has been studied for use in such microelectronic applications. Such studies have included the different forms of barium titanate including powder, bulk, thin film and multilayer owing to their excellent electronic and optical characteristics including high dielectric constant, transparency in visible wavelength, and high non-linear optical susceptibility.
The use of barium titanates in electric vehicles is further highly desired. Presently, automotive internal combustion engines are increasingly being challenged by environmental concerns, favoring an increased role for electric vehicles. Thus, supercapacitors, as well as batteries, play a major role in this developing market.
Supercapacitors having capacitances in the range of milli-Farads to Farads have suffered from slow charging and discharging cycles in light of their high series resistance (i.e., large RC time constants). In addition, they often rely on corrosive and environmentally unfriendly electrolytes. For instance, the BaTiO3 thin films set forth in T. Hayashi, Jpn. J. Appl. Phys., 32 4092 (1993) have a capacitance unacceptable for use in electric vehicles as well as other industries. Alternative nanosized capacitors are constantly being sought.
Need exists therefore for an electrical energy storage device that combines the desirable features of conventional capacitors yet can store much larger amounts of energy in a smaller package and can be manufactured at reasonable costs.
The invention relates to a nanostructured BaTiO3 thin film composite that has from 1,000 to 10,000 times the area and storage capacity of conventional BaTiO3 thin films, plates and arrays. The BaTiO3thin films and plates of the invention can also exhibit a variable discharge rate controlled by optical illumination (pumping).
The barium titanates comprising the coating of the thin films or plates of the invention exhibit dielectric, ferroelectric and/or paraelectric properties. The barium titanates are of the formula BaaTibOc wherein a and b are independently between 0.75 and 1.25 and c is 2.5 to about 5.0. The thin film composites of the invention exhibit a storage capacity of at least 1 to 100 farads per cubic centimeter.
In another embodiment of the invention, the thin films comprise barium titanate incorporating a non-reactive electroconductive material, xe2x80x9cMxe2x80x9d, capable of forming a microstructure with the thin film. The resulting titanate is of the formula MdBaaTibOc wherein d is about 0.01 to about 0.25, a is about 0.75 to about 1.25, b is about 0.75 to about 1.25 and c is about 2.5 to about 5.0. Thin film composites containing the incorporated material have a storage capacity of a magnitude between 10 to 1,000 times higher than the storage capacity of the composite materials without incorporated xe2x80x9cMxe2x80x9d (BaaTibOc).
The thin film composites of the invention have particular applicability in the production of microminiature capacitors.
Lastly, the invention relates to a process of preparing and using a barium titanate film composite, optionally incorporating particles of xe2x80x9cMxe2x80x9d.